Abstract
4-Coumarate:coenzyme A ligase (4CL; EC 6.2.1.12) is a key enzyme in the phenylpropanoid metabolic pathways for monolignol and flavonoid biosynthesis. 4CL has been much studied in dicotyledons, but its function is not completely understood in monocotyledons, which display a different monolignol composition and phenylpropanoid profile. In this study, five members of the 4CL gene family in the rice (Oryza sativa) genome were cloned and analyzed. Biochemical characterization of the 4CL recombinant proteins revealed that the rice 4CL isoforms displayed different substrate specificities and catalytic turnover rates. Among them, Os4CL3 exhibited the highest turnover rate. No apparent tissue-specific expression of the five 4CLs was observed, but significant differences in their expression levels were detected. The rank in order of transcript abundance was Os4CL3 > Os4CL5 > Os4CL1 > Os4CL4 > Os4CL2. Suppression of Os4CL3 expression resulted in significant lignin reduction, shorter plant growth, and other morphological changes. The 4CL-suppressed transgenics also displayed decreased panicle fertility, which may be attributed to abnormal anther development as a result of disrupted lignin synthesis. This study demonstrates that the rice 4CLs exhibit different in vitro catalytic properties from those in dicots and that 4CL-mediated metabolism in vivo may play important roles in regulating a broad range of biological events over the course of rice growth and development.
Highlights
4-Coumarate:coenzyme A ligase (4CL; EC 6.2.1.12) is a key enzyme in the phenylpropanoid metabolic pathways for monolignol and flavonoid biosynthesis. 4CL has been much studied in dicotyledons, but its function is not completely understood in monocotyledons, which display a different monolignol composition and phenylpropanoid profile
In gymnosperms and dicotyledonous angiosperms, the catalytic properties of 4CL isoforms have been studied extensively. 4CL isoforms with different substrate affinities may direct metabolic flux through different pathways to synthesize a variety of phenolic compounds, such as different monolignols, flavonoids, isoflavonoids, coumarins, suberin, and wallbound phenolics (Boerjan et al, 2003; Naoumkina et al, 2010)
This paper presents a characterization of the 4CL gene family in japonica rice and shows that 4CLs play a role in regulating a broad range of biological events throughout the life cycle of rice
Summary
4-Coumarate:coenzyme A ligase (4CL; EC 6.2.1.12) is a key enzyme in the phenylpropanoid metabolic pathways for monolignol and flavonoid biosynthesis. 4CL has been much studied in dicotyledons, but its function is not completely understood in monocotyledons, which display a different monolignol composition and phenylpropanoid profile. 4-Coumarate:coenzyme A ligase (4CL; EC 6.2.1.12) is a key enzyme in the phenylpropanoid metabolic pathways for monolignol and flavonoid biosynthesis. Five members of the 4CL gene family in the rice (Oryza sativa) genome were cloned and analyzed. Biochemical characterization of the 4CL recombinant proteins revealed that the rice 4CL isoforms displayed different substrate specificities and catalytic turnover rates. Suppression of Os4CL3 expression resulted in significant lignin reduction, shorter plant growth, and other morphological changes. This study demonstrates that the rice 4CLs exhibit different in vitro catalytic properties from those in dicots and that 4CLmediated metabolism in vivo may play important roles in regulating a broad range of biological events over the course of rice growth and development. This paper presents a characterization of the 4CL gene family in japonica rice and shows that 4CLs play a role in regulating a broad range of biological events throughout the life cycle of rice
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